The present invention relates to a process for the economical recovery of light mixed hydrocarbon components from the air-hydrocarbon vapor mixture which arises as a result of the vapor-liquid equilibrium established in a partially filled liquid hydrocarbon vessel. "Breathing" of the vessel or loading or refilling of same results in expulsion of an air-hydrocarbon vapor mixture to the atmosphere, polluting the environment, and creating a potential fire hazard. Common loading facilities involving crude oil storage tanks, truck and marine tankers, underground service station tanks, and numerous other industrial operations all have potential for such pollution and fire hazard. A means of controlling said pollution of the atmosphere thus becomes desirable and even required in some parts of the country where gasoline vapor emissions from service stations combined with high concentrations of photochemical oxidants in the atmosphere create smog problems. The economics of the losses resulting from the escaped hydrocarbons indicate need for a system whereby said hydrocarbon may be recovered for further use.
Various means have been devised for coping with hydrocarbon laden air, such as the vapor recovery and disposal system disclosed in U.S. Pat. No. 3,897,193. This particular process utilizes solid adsorbent beds for removal of the hydrocarbons from the air-hydrocarbon mixture, desorption of the hydrocarbon, and subsequent incineration thereof. Such a system requires a high investment; and in the event of the production of small quantities of hydrocarbon vapor, the heat derived from the incineration may not justify the expense of the equipment required. Furthermore, such an installation is impractical for a local service station which has little or no use for the heat produced. Numerous other methods, such as are disclosed in U.S. Pat. No. 3,455,089, U.S. Pat. No. 3,543,484, and U.S. Pat. No. 3,776,283, teach the adsorption of the hydrocarbon components from an air-hydrocarbon mixture, but fail to disclose, teach, or otherwise suggest a means for the economical recovery of said components.
The hydrocarbon recovery problems associated with all adsorbent systems lies in the varying vapor composition of the desorption stream during regeneration of the adsorbent bed. During the regeneration step, regardless of the method of regeneration chosen, the lightest hydrocarbons are desorbed first and followed by progressively heavier molecules until the heaviest components are extracted. The resulting continual change in regeneration vapor composition has heretofore hampered economical recovery of the hydrocarbon components.
Accordingly, it is an object of this invention to provide a method for the economical recovery of hydrocarbon components from an air-hydrocarbon mixture, thus achieving economies in the control of air pollution.